Piezoelectrically actuated mems optical device having a protected chamber and manufacturing process thereof

ABSTRACT

A MEMS optical device having an optically active portion and an actuation portion adjacent to each other. The MEMS optical device includes a body, a piezoelectric actuator, and a cap. The body is formed by a substrate, housing a cavity containing a fluid and by a deformable region fixed to the substrate, suspended over the cavity and forming a membrane. The piezoelectric actuator extends on the deformable region at the actuation portion and is protected by the cap, which is coupled to the body at the actuation portion and defines a chamber that houses the piezoelectric actuator.

BACKGROUND Technical Field

The present disclosure relates to a piezoelectrically actuated MEMS(Micro-Electro-Mechanical System) device. In some embodiments, referenceis made to piezoelectrically actuated MEMS optical devices hereinafter.

Description of the Related Art

As is suitable, actuators are devices that convert a physical quantityof one type into another of a different type; in some embodiments, thequantity deriving from conversion usually entails some form of movementor mechanical action.

Recently, actuators of micrometric and nanometric dimensions, alsoreferred to as micro-actuators or nano-actuators, which can be obtainedwith semiconductor technology (the so-called MEMS devices) and hence atvery contained costs have been proposed. These micro-actuators andnano-actuators can be used in a variety of devices, in some instances inmobile and portable devices.

Examples of microactuators are valves, switches, pumps, linear androtary micromotors, linear positioning devices, speakers, and opticaldevices.

Microactuators basically work according to four physical principles:

-   -   Electrostatic microactuators: they exploit the attraction        between conductors charged in an opposite way;    -   Thermal microactuators: they exploit the displacement caused by        thermal expansion or contraction;    -   Piezoelectric microactuators: they exploit the displacement        caused by strains and stresses induced by electrical fields; and    -   Magnetic microactuators: they exploit the displacement caused by        the interaction between different elements having magnetic        characteristics, such as permanent magnets, external magnetic        fields, magnetisable materials, and conductors of electric        current.

Each technology presents advantages and limits in terms of powerconsumption, movement rapidity, force exerted, movement amplitude,movement profile, simplicity of manufacture, amplitude of the appliedelectrical signals, strength and sensitivity, which makes use thereofadvantageous in certain applications, but not in others, and hencedetermine the field of use.

Hereinafter, an actuator device obtained with MEMS technology, whichoperates according to a piezoelectric principle and is able to exploitMEMS thin-film piezo (TFP) technology is considered.

MEMS thin film piezo technology currently uses a unimorphic actuationmode, wherein a structure (for example, a membrane, a beam, or acantilever beam), usually formed by at least two superimposed layers,undergoes bending as a result of variations in the applied load. In thiscase, there is a controlled alteration of the strain in one of thelayers, referred to as “active layer”, which causes a passive strain inthe other layer or layers, also referred to as “inactive layers” or“passive layers”, with consequent bending of the structure.

The above technique is used for bending the membrane, the beam, or thecantilever in applications where a vertical movement is desired, i.e., amovement in a direction perpendicular to the plane of lie of thestructure, such as liquid-jet printing heads, auto-focus systems,micro-pumps, microswitches, and speakers.

For instance, FIGS. 1A and 1B illustrate a cantilever 1 constrained at afirst end 2 and free to bend at a second end 3. The cantilever 1 is hereformed by a stack of layers including a supporting layer 5, for examplemade of a semiconductor material of a first type of conductivity, forexample P; an active layer 6, for example made of piezoelectric material(PZT); and a top layer 7, for example made of a semiconductor materialof a second type of conductivity, for example N.

In the presence of reverse biasing, as illustrated in FIG. 1B, theapplied electrical field causes strains in the cantilever 1, whichgenerates a bending of the free end 3 downwards.

An example of embodiment of a piezoelectric MEMS actuator applied to ageneric optical device is illustrated in FIGS. 2A and 2B. Here, theoptical device, designated by 10, comprises a deformable part ormembrane 15, for example, made of glass (e.g., BPSG—BoroPhosphoSilicateGlass), resting, through a lens element 11 (made, for example, ofpolymer), on a support 12 which is also, for example, made of glass;furthermore, the membrane 15 carries two piezoelectric regions 13arranged at a distance from each other.

In absence of biasing, FIG. 2A, the membrane 15 and the lens element 11have planar surfaces and do not modify the path of a light beam 16 thatcrosses them. When the piezoelectric regions 13 are biased, FIG. 2B,they cause a deformation of the membrane 15. Deformation of the centralarea of the membrane 15 is transmitted to the lens element 11, the topsurface of which curves, thus modifying the focus of the lens element 11and therefore the path of the light beam 16. It is therefore possible tomodify the optical transmission characteristics of the optical device10.

An example of MEMS devices for optical applications are auto-focus MEMSdevices, such as, for example, liquid lenses; in particular liquidlenses are optical devices, the lens of which is formed by a liquidmaterial (for example, apolar liquids, water-based liquids or liquidcrystals). Liquid lenses are able to modify in an adaptive way theirfocus by exploiting various physical principles; in particular, liquidlenses may be based, for example, on the electrostatic actuationprinciple, on electrowetting, on electrophoresis, or on magnetic orpiezoelectric actuation principle.

In particular, piezoelectrically actuated liquid lenses have a structuresimilar to that of the optical device 10 of FIGS. 2A and 2B. Inparticular, the lens element 11 is a liquid, for example oil, and themembrane 15 is anchored to the support 12 so as to form a cavity adaptedto contain the lens element 11. In use, piezoelectrically actuatedliquid lenses operate in a way similar to what is described withreference to FIGS. 2A and 2B.

The piezoelectric actuators illustrated in FIGS. 1A, 1B, 2A, and 2B havethe advantage of being fast and compact devices. In fact, unlike othertypes of actuators, such as capacitive and/or magnetic actuators, theydo not require further structures, such as electrodes connected to areference potential (as in the case of capacitive actuators) or magnetsand/or coils (as in the case of magnetic actuators).

However, MEMS optical devices, in particular liquid lenses, of a knowntype described above have some disadvantages.

In particular, currently, piezoelectric actuators are exposed to theexternal environment and may therefore be subject to mechanical stresses(such as, for example, impact, mechanical shock, dropping) or of achemical type (for example, corrosion, oxidation). These stresses maysignificantly reduce the performances of piezoelectric actuators, aswell as of the MEMS optical device itself. Furthermore, piezoelectricactuators (and therefore the MEMS optical device) are less reliableduring use.

BRIEF SUMMARY

In some embodiments, the present disclosure provides a MEMS opticaldevice and a manufacturing process thereof.

In some embodiments, the present disclosure provides a piezoelectricallyactuated MEMS optical device and a manufacturing process thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, a preferredembodiment thereof is now described, purely by way of non-limitingexample, with reference to the attached drawings, wherein:

FIGS. 1A and 1B show simplified side views of an example piezoelectricMEMS actuator, respectively, in a rest condition and a condition ofdeformation;

FIGS. 2A and 2B show simplified side views of another examplepiezoelectric MEMS actuator, used in an optical device in a restcondition and a condition of deformation, respectively;

FIG. 3 is a cross-section view taken along the section line of FIG. 4 ofthe present MEMS optical device;

FIG. 4 is a schematic top plan view of the MEMS optical device of FIG. 3with removed and transparent parts;

FIG. 5 is a simplified perspective view of the MEMS optical device ofFIGS. 3-4 with removed parts;

FIGS. 6-10, 12, 14, and 15 are cross-section views, similar to that ofFIG. 3, of the MEMS optical device of FIGS. 3-5 in successivemanufacturing steps;

FIGS. 11 and 13 are top plan views of the present MEMS optical device inthe manufacturing steps of FIGS. 11 and 12, respectively; and

FIG. 16 shows a block diagram of an electronic apparatus including theMEMS optical device of FIGS. 3 to 5.

DETAILED DESCRIPTION

FIGS. 3 and 4 are schematic illustrations of a MEMS optical device 30according to an embodiment; in some embodiments, the MEMS optical device30 is a liquid lens for auto-focus applications.

The MEMS optical device 30 generally has a parallelepipedal shape,having a quadrangular shape (for example, rectangular) in top plan view(FIG. 4), and has a base defining a plane A parallel to an XY plane of acartesian reference system XYZ. Furthermore, the MEMS optical device 30has an symmetry axis S, parallel to a Z axis of the cartesian referencesystem XYZ, and a centre O, lying on the symmetry axis S.

With reference to FIGS. 3 and 4, the MEMS optical device 30 comprises acentral portion 30A and a peripheral portion 30B.

The MEMS optical device 30 comprises, FIG. 3: a body 31, having a firstand a second surface 31A, 31B; and a cap 33. The body 31 and the cap 33are coupled together by means of a first intermediate layer 35 (forexample, a layer of benzocyclobutane, BCB, resin, of silicon oxide,SiO₂).

The body 31 comprises a substrate 32 and a deformable region 52,extending over the substrate 32 on the peripheral portion 30B.

The substrate 32 houses a cavity 45, adapted to contain a fluid 49 (forexample, an immersion liquid, in some embodiments immersion oil, such asthe material produced by Solvay under the trade name Fomblin®). Thecavity 45 comprises a first and a second cavity portion 45A, 45B,arranged, respectively, at the central portion 30A and at the peripheralportion 30B of the MEMS optical device 30 and in fluidic connection withone another.

In greater detail, the substrate 32 comprises a support 41, a firstcavity-definition layer 43 and a second cavity-definition layer 50.

The support 41 is, for example made of a material transparent to thevisible light, such as glass (for example, BPSG), and delimits thecavity 45 at the bottom.

The first cavity-definition layer 43 is made of dielectric material (forexample, a dry film, such as SINR® manufactured by Shin-Etsu, in someembodiments SINR®-3170), extends over the support 41 on the peripheralportion 30B of the MEMS optical device 30 and has, in top plan view, forexample an annular shape with centre O and symmetry axis S, asrepresented by the dashed line in FIG. 4.

In some embodiments, the first cavity-definition layer 43 has arectangular outer perimeter, coinciding with that of the MEMS opticaldevice 30, and a circular inner perimeter, having a first diameter d₁and coupled to the support 41 by means of a second intermediate layer 47(made, for example, of BPSG or BCB resin).

The second cavity-definition layer 50, made of dielectric material (forexample, a film that can be deposited via spin-coating), extends overthe first cavity-definition layer 43 on the peripheral portion 30B andhas, in top plan view, FIG. 4, an annular shape with centre O andsymmetry axis S.

In some embodiments, the second cavity-definition layer 50 has arectangular outer perimeter, coinciding with that of the MEMS opticaldevice 30, and a circular inner perimeter, having a second diameter d₂greater than the first diameter d₁ (see also FIG. 4). Consequently, thefirst cavity-definition layer 43 projects towards the centre O withrespect to the second cavity-definition layer 50.

The substrate 32 further comprises a plurality of structural elements 51(see, in some embodiments, FIG. 4), radially extending straddling theinner perimeter of the first cavity-definition layer 43; in someembodiments, here, each structural element 51 has for example arectangular shape in top plan view. Furthermore, the structural elements51 are angularly equidistant from one another so as to form a radialarrangement about the central portion 30A.

The first cavity-definition layer 43 and the second cavity-definitionlayer 50 delimit, at the sides, the cavity 45 and the structuralelements 51 separate the first cavity portion 45A from the second cavityportion 45B. In some embodiments, the first cavity portion 45A isdelimited by the first cavity-definition layer 43 and by the structuralelements 51 at the sides, at the bottom by the support 41, and at thetop by the deformable region 52; the second cavity portion 45B isdelimited by the second cavity-definition layer 50 and by the structuralelements 51 at the sides, at the bottom by the first cavity-definitionlayer 43, and at the top by the deformable region 52. In practice, thesecond cavity portion 45B surrounds the top part of the first cavityportion 45A and is fluidically connected to the latter at the gapsbetween the structural elements 51.

The deformable region 52 of the body 31 extends over the secondcavity-definition layer 50 and the plurality of structural elements 51.In some embodiments, the deformable region 52 extends over the cavity 45and forms a membrane 57. The membrane 57 comprises a first and a secondmembrane portion 57A, 57B, arranged at the central portion 30A (over thefirst cavity portion 45A) and at the peripheral portion 30B of the MEMSoptical device 30 (over the second cavity portion 45B) respectively.

The deformable region 52 is formed by a first and by a second flexiblelayer 55, 60.

In some embodiments, the first flexible layer 55 is made of polymer (forexample, cellophane, polyethylene, or patternable silicones, whichextends throughout the entire first surface 31A of the body 31 anddelimits the cavity 45 at the top. In addition, the first flexible layer55 comprises a first and a second region 55′, 55″, suspended over thefirst and the second cavity portion 45A, 45B respectively; in someembodiments, the first region 55′ forms the first membrane portion 57A.

The second flexible layer 60 is of semiconductor material (for example,epitaxial polysilicon) and extends to the peripheral portion 30B of theMEMS optical device 30 over the second cavity portion 45B; in greaterdetail, in top plan view, FIG. 4, the second flexible layer 60 has anannular shape with a centre O.

The second region 55″ of the first flexible layer 55 and the secondflexible layer 60 form the second membrane portion 57B.

A first dielectric layer 61, made, for example, of SiO₂, extends overthe second flexible layer 60 and has a shape congruent therewith.

A piezoelectric actuator 40 extends over the first dielectric layer 61and is formed by a stack of layers. In some embodiments, the stack oflayers comprises a first electrode 70; a piezoelectric region 71, forexample of PZT (Pb, Zr, TiO₂) or AN, extending on the first electrode70; and a second electrode 72, extending on the piezoelectric region 71.

The piezoelectric actuator 40 further comprises first and secondconductive paths 80, 82, extending from the first and from the secondelectrodes 70, 72 towards a first and a second contact pad 100, 102 forexternal connection by means of bonding wires (not illustrated)respectively. In some embodiments, the first and the second conductivepaths 80, 82 are electrically insulated from each other and from thesecond flexible layer 60 by means of one or more passivation layers 75made of dielectric material.

The cap 33 of the MEMS optical device 30 has for example an annularshape with center O and with symmetry axis S in top plan view (notillustrated in FIG. 4 for reasons of clarity). The cap 33, together withthe second membrane portion 57B, surrounds an optical opening 90 of acircular shape, with centre O and radius R₁. In practice, the opticalopening 90 is arranged at the central portion 30A of the MEMS opticaldevice 30. In the illustrated embodiment, the radius R₁ is approximatelyequal to the first diameter d₁ of the first cavity portion 45A so thatthe optical opening 90 is aligned to, and substantially has the samearea as, the first cavity portion 45A.

The cap 33 comprises a first and a second structural layer 34, 37,coupled together by means of a third intermediate layer 39 (made, forexample, of SiO₂). In some embodiments, the first structural layer 34 ismade of semiconductor material, such as silicon, and the secondstructural layer 37 is made of semiconductor material, such as epitaxialpolysilicon.

The first structural layer 34 houses a chamber 42, adapted to containthe piezoelectric actuator 40 of the body 31; in some embodiments, thechamber 42 has, in top plan view (not illustrated), an annular shapewith centre O and symmetry axis S.

A second dielectric layer 36, made of insulating material (for example,SiO₂), is interposed between the first intermediate layer 35 and thefirst structural layer 34.

The cap 33 enables insulation of the piezoelectric actuator 40 both fromthe external environment and from the cavity 45, and therefore from thefluid 49, protecting it from possible mechanical and/or chemicalstresses.

In use, a potential difference is applied between the first and thesecond electrodes 70, 72 of the piezoelectric actuator 40 so as togenerate a deflection of the second membrane portion 57B in a downwardsdirection (towards the inside of the cavity 45). Deflection of thesecond membrane portion 57B causes a compression of the fluid 49 in thesecond cavity portion 45B and its displacement towards the first cavityportion 45A. Consequently, the liquid in the first cavity portion 45Apresses on the first membrane portion 57A, deforming and deflecting ittowards the outside of the cavity 45.

FIG. 5 shows the MEMS optical device 30 in the deformed conditiondescribed above. As may be noted, the second membrane portion 57B isdeflected downwards, and the first membrane portion 57A is deflectedupwards.

In this way, it is possible to modify the focus of the optical opening90 of the present MEMS optical device 30, in a way similar to what isdescribed with reference to FIGS. 2A and 2B. In some embodiments, thepresence of a greater or smaller amount of fluid 49 in the first cavityportion 45A (and therefore in the central portion 30A of the MEMSoptical device 30) enables modification of the properties of the opticalopening 90, with consequent modification of the optical path of a lightbeam (not illustrated) crossing the fluid 49.

The MEMS optical device 30 of FIGS. 3-5 may be manufactured according tothe manufacturing steps illustrated in FIGS. 6-17.

In detail, FIG. 6 shows a first wafer 200, having a top surface 200A anda bottom surface 200B. In some embodiments, the first wafer 200 ismanufactured according to manufacturing steps similar to those describedin U.S. patent US 2014/0313264 A1. Consequently, the manufacturing stepsof the first wafer 200, common to the patent referred to above, arebriefly described hereinafter.

In some embodiments, the first wafer 200 comprises a supportingsubstrate 202, made of semiconductor material (for example, silicon);and a stack of membrane layers 210, formed on the supporting substrate202 and comprising a first insulating layer 204, made, for example, ofsilicon oxide; the second flexible layer 60 of FIG. 3; and the firstdielectric layer 61 of FIG. 3.

In some embodiments, the first insulating layer 204 and the secondinsulating layer 61 are formed according to suitable growth ordeposition techniques, for example thermal growth, and have a thicknessranging, for example, between 0.1 and 2 μm. Furthermore, the secondflexible layer 60 is epitaxially grown in a suitable way and has athickness ranging between 1 and 50 μm.

In alternative embodiments, the stack of membrane layers 210 may bemanufactured with other materials which are typically used for MEMSdevices, for example SiO₂, SiON, or SiN, with a thickness rangingbetween 0.5 and 10 μm, or by a stack in various combinations ofSiO₂—Si—SiN.

The first electrode 70, made, for example, of titanium oxide (TiO₂),with a thickness ranging between 5 and 50 nm and platinum (Pt), with athickness ranging between 30 and 300 nm; the piezoelectric region 71,for example with a thickness ranging between 0.5 and 3 μm; and thesecond electrode 72, made, for example, of platinum (Pt), iridium (Ir),iridium oxide (IrO₂), an tungsten and titanium alloy (TiW), or ruthenium(Ru), with a thickness ranging between 30 and 300 nm extend over the topsurface 200A of the first wafer 200.

Furthermore FIG. 6 shows the passivation layers 75 covering the firstelectrode 70, the piezoelectric region 71, the second electrode 72, andthe second flexible layer 60, the first and the second conductive paths80, 82, and the first and the second contact pads 100, 102. In someembodiments, the passivation layers 75 have a thickness ranging, forexample, between 10 nm and 1000 nm, and the first and the secondconductive paths 80, 82 and the first and the second contact pads 100,102 are made of conductive material, for example metal (such as aluminum(Al) or gold (Au) eventually in combination with barrier and adhesionlayers, such as Ti, TiN, TiW or Ta, TaN).

A second wafer 220 is manufactured so as to form the cap 33. In someembodiments, the second wafer 220 comprises the first and the secondstructural layers 34, 37, as well as the second dielectric layer 36.

For instance, the first structural layer 34 has a thicknessapproximately 400 μm, and the second structural layer 37 has a thicknessranging between approximately 1 μm and approximately 20 μm. In someembodiments, the second structural layer 37 is approximately 4 μm.

Furthermore, the second wafer 220 has a first and a second trench 255′,255″, as well as a recess 260, designed to form the chamber 42. Thetrenches 255′, 255″ and the recess 260 are obtained by means of suitableetching techniques by selectively removing portions of the seconddielectric layer 36 and of the first structural layer 34, in a singleetching step, or in successive etching steps. The trenches 255′, 255″have a depth ranging, for example, between 50 and 300 μm.

Next, FIG. 8, the first and the second wafers 200, 220 are coupled bymeans of the first intermediate layer 35 so that the recess 260surrounds the piezoelectric actuator 40 formed on the top surface 200Aof the first wafer 200, thus forming the chamber 42. Furthermore, as aresult of the gluing step, the second trench 255″ houses the first andthe second contact pads 100, 102 (the latter not being visible), thusforming a contact-containment chamber 304.

Next, a grinding step is carried out on the supporting substrate 202starting from the bottom surface 200B of the first wafer 200 so as toreduce the thickness of the supporting substrate 202, for example, downto 20 μm. Then, a step of silicon anisotropic etching is carried out soas to completely remove the residue of the supporting substrate 202.Thanks to the fact that reduction in the thickness of the first wafer200 is carried after the step of coupling between the first and thesecond wafers 200, 220, it is not particularly critical or difficult;moreover, the structures (piezoelectric actuator 40 and contact pads100, 102) are protected in the chamber 42 and in the contact-containmentchamber 304.

Next, FIG. 9, the structure of FIG. 8 is overturned and subjected to afurther step of definition of a suitable type, for example, alithographic step; in some embodiments, the first insulating layer 204is patterned so as to form an opening 355A, exposing the second flexiblelayer 60 at least in part.

Then, a membrane layer 355 of photopatternable spin-on silicone isdeposited using, for example, suitable deposition techniques for athickness, for example, ranging between 5 and 50 μm. The membrane layer355 and the first insulating layer 204 are designed to form the firstflexible layer 55 of FIG. 3.

Next, FIG. 10, the second cavity-definition layer 50 and the structuralelements 51 of FIGS. 3 and 4 are formed, as illustrated alsoschematically in the top plan view of FIG. 11. For this purpose, a layerof dielectric material in liquid or sol-gel is deposited and definedusing suitable deposition techniques, such as, for example,spin-coating.

Then, FIGS. 12 and 13, the first cavity-definition layer 43 of FIG. 3 isobtained, using suitable deposition techniques, for example, lamination,and photolithographic definition. In this step, the cavity 45 of FIGS.3-5 is also formed and is subsequently filled with the fluid 49.

Next, FIG. 14, the support 41 is coupled (in some embodiments, glued) tothe first cavity-definition layer 43 via the second intermediate layer47 to form the body 31.

Then, FIG. 15, the second structural layer 37 is thinned out, forexample using suitable grinding techniques, so as to reduce thethickness, for example, down to 150 μm. Next, using a mask layer (notillustrated) and suitable photolithographic and etching techniques, thethinned out second structural layer 37, the third intermediate layer 39,and the first structural layer 34 are etched. For instance, anisotropicetching such as DRIE (Deep Reactive Ion Etching) is initially performed,until the second flexible layer 60 is reached, and wet etching of thelatter is then carried out, thus leaving the membrane layer 355 made ofpolymeric material exposed. At the end of the manufacturing stepdescribed above, the optical opening 90 is formed.

Finally, a step of partial sawing of the sole second wafer 220, along acutting line 510 illustrated dashed in FIG. 15, enables removal of anedge portion of the second wafer 220 at the contact pads 100, 102, so asto render them accessible from outside for a subsequent wire-bondingoperation.

Before or after the partial-sawing step, the first wafer 200 is alsosawed so as to form the MEMS optical device 30 of FIGS. 3 to 5.

FIG. 16 shows an electronic device 600 that uses the MEMS optical device30 of FIGS. 3-5.

The electronic device 600 comprises, in addition to the MEMS device 30,a microprocessor (CPU) 601, a memory block 602, connected to themicroprocessor 601, and an input/output interface 603, for example akeypad and/or a display, which is also connected to the microprocessor601. An ASIC 604 may be integrated in the MEMS device 30 or arrangedoutside the MEMS device 30 and operatively coupled thereto.

The MEMS device 30 communicates with the microprocessor 701 via the ASIC604.

The electronic device 600 is, for example, a mobile communicationdevice, such as a mobile phone or smartphone, a PDA, a computer, asmartwatch, but may also be a voice recorder, an audio-file reader withvoice-recording capacity, a console for video games, and the like.

The present MEMS optical device and the manufacturing method thereofpresent various advantages.

In some embodiments, the chamber 42 of the second wafer 220 enablesisolation of the piezoelectric actuator 40 both from the externalenvironment and from the cavity 45 (and, therefore, from the fluid 49)so as to protect it from possible external mechanical and/or chemicalstresses. Consequently, the actuation capacity of the piezoelectricactuator 40, and hence the performance of the MEMS optical device 30,are not affected by external stresses. It is hence reliable even overtime.

Moreover, the manufacturing method used for manufacturing the presentMEMS optical device 30 is simple and far from costly.

Finally, it is clear that modifications and variations may be made tothe MEMS device and to the manufacturing process described andillustrated herein, without departing from the scope of the presentdisclosure, as defined in the annexed claims.

For instance, the materials used for manufacturing of the MEMS opticaldevice 30 may be different from the ones referred to in the presentdescription.

In addition, the structural elements 51 may have shapes different fromthose illustrated in FIGS. 4 and 11; for example, they may be shapedlike a cross, cylindrical pillars, or semi-arches.

The peripheral portion and the central portion could be swapped roundand/or could form an actuation portion and an optical portion of adifferent shape, according to the desired optical effects.

The various embodiments described above can be combined to providefurther embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A MEMS optical device, the MEMS optical device comprising: asubstrate, the substrate housing a first cavity containing a fluid; adeformable structure coupled to the substrate, the deformable structureincluding a first portion and a second portion, the first portion of thedeformable structure being suspended over the first cavity; apiezoelectric actuator over the second portion of the deformablestructure; and a cap coupled to the second portion of the deformablestructure and defining a chamber housing the piezoelectric actuator. 2.The device according to claim 1, wherein the deformable structureincludes: a first flexible layer covering the first cavity and includinga first region and a second region, the first region being arrangedadjacent to the first cavity, and the second region being arrangedadjacent to the piezoelectric actuator; and a second flexible layer overthe second region of the first flexible layer; wherein the first regionof the first flexible layer forms a first membrane, and wherein thesecond region of the first flexible layer and the second flexible layerform a second membrane.
 3. The device according to claim 2, wherein thefirst flexible layer is a transparent polymeric material.
 4. The deviceaccording to claim 2, wherein the second flexible layer is epitaxialpolysilicon.
 5. The device according to claim 2, wherein the substratefurther includes a second cavity, the second cavity being arrangedadjacent to the second region of the first flexible layer, wherein thefirst membrane is suspended over the first cavity, and the secondmembrane is suspended over the second cavity.
 6. The device according toclaim 5, wherein the second cavity has an annular shape and surroundsthe first cavity.
 7. The device according to claim 6, wherein thesubstrate includes: a support of transparent material; a firstcavity-definition layer extending over the support and surrounding thefirst cavity; a second cavity-definition layer extending at leastpartially over the first cavity-definition layer and surrounding thesecond cavity; and a plurality of structural elements over the firstcavity-definition layer and straddling between the first cavity and thesecond cavity; wherein the second cavity-definition layer and thestructural elements contact the deformable structure.
 8. The deviceaccording to claim 1, wherein the cap includes a structural layer ofsemiconductor material.
 9. An electronic apparatus, comprising: the MEMSdevice; an ASIC, electrically coupled to the MEMS device; a memoryblock; an input/output interface; and a microprocessor, electricallycoupled to the ASIC, the memory block and the input/output interface;wherein the MEMS device includes: a first body, the first body housing afirst cavity and a second cavity laterally adjacent to one another, thefirst cavity containing a fluid, a first flexible layer coupled to thefirst body, the first flexible layer including a first region coveringthe first cavity and a second region covering the second cavity, apiezoelectric actuator over the second region of the first flexiblelayer, and a second body over the second region of the first flexiblelayer and defining a chamber housing the piezoelectric actuator, thefirst region of the first flexible layer being at least partiallyexposed from the second body.
 10. The electronic apparatus of claim 9,wherein the MEMS device further includes a second flexible layer betweenthe second region of the first flexible layer and the piezoelectricactuator.
 11. The electronic apparatus of claim 9, wherein the secondcavity surrounds the first cavity.
 12. The electronic apparatus of claim9, wherein the second cavity is shallower than the first cavity.
 13. Amethod for manufacturing a MEMS optical device, the method comprising:forming a body housing a cavity in a substrate, a deformable structurefixed to the substrate, the deformable structure having a first portionsuspended over the cavity and a second portion surrounding the firstportion, and a piezoelectric actuator adjacent to the second portion ofthe deformable structure; forming a cap having a chamber; and couplingthe cap to the second portion of the deformable structure, the chamberof the cap enclosing the piezoelectric actuator.
 14. The methodaccording to claim 13, wherein the forming the body includes: forming,on a first wafer, the piezoelectric actuator; forming the deformablestructure by thinning out the first wafer; and forming the substrateover the deformable structure.
 15. The method according to claim 13,wherein the forming the cap includes: arranging a second wafer having afirst structural layer of a semiconductor material and a secondstructural layer coupled to the first structural layer by means of anintermediate layer; forming a first trench and a second trench in thefirst structural layer; and forming the chamber in the first structurallayer, laterally with respect to the first trench and the second trench.16. The method according to claim 15, further comprising, prior toforming the deformable structure, coupling the first wafer and thesecond wafer.
 17. The method according to claim 16, wherein the formingthe piezoelectric actuator includes: forming, on a supporting substrate,a stack of membrane layers having a first insulating layer, a firstmembrane layer, and a second insulating layer; forming, on the stack ofmembrane layers, a first electrode layer, a piezoelectric layer, and asecond electrode layer; and forming a first contact pad and a secondcontact pad in electrical contact with the first electrode layer and thesecond electrode layer, respectively, and in a position such that thefirst contact pad and the second contact pad are housed in the secondtrench during the coupling of the first wafer and the second wafer. 18.The method according to claim 17, wherein the forming the deformableregion includes: removing the supporting substrate; forming an openingby removing selective portions of the first insulating layer, theopening exposing the first portion of the at least in part; and forminga second membrane layer, extending over the first insulating layer andin the opening, the first membrane layer and the second membrane layerforming a membrane.
 19. The method according to claim 18, wherein theforming the substrate includes: forming a first delimitation layer onthe second membrane layer; forming a second cavity-definition layer anda plurality of structural elements by removing selective portions of thefirst delimitation layer; forming a second delimitation layer over thefirst delimitation layer; forming a first cavity-definition layer byremoving selective portions of the second delimitation layer, the firstand the second cavity-definition layers delimiting the cavity; fillingthe cavity with a fluid; and closing the cavity by coupling a support tothe first cavity-definition layer.
 20. The method according to claim 17,further comprising: exposing the first and the second contact pads byremoving selective portions of the second wafer, the first membranelayer and the second insulating layer; and forming an optical opening byremoving selective portions of the second insulating layer, the firstmembrane layer being exposed from the optical opening.